FIG. 1 illustrates a prior art filter system 10 for a diesel engine 12. An exhaust line 14 is provided between the diesel engine 12 and the filter system 10. The filter system may include a housing 16 that includes at least a first section 18 and a second section 20. The first section 18 typically includes a flow-through monolith 22 therein and wherein the flow-through monolith is coated with a catalyst such as platinum. The exhaust gas from the diesel engine 12 includes a variety of constituents including NO and particulate matter which typically is in the form of a carbon-based material. The catalyst on the flow-through monolith 22 promotes the reaction of the NO with oxygen also present in the exhaust gas to form NO2. However, the reaction is not efficient enough to completely convert all of the NO in the exhaust gas to NO2. Thus, as shown in FIG. 1, both NO and NO2 leave the first section 18 of the filter and enter the second section 20 of the filter system. The second section 20 typically includes a wall flow monolith 24 therein. Wall flow monoliths are known to those skilled in the art and typically are manufactured from a ceramic material in a manner to provide a plurality of through hole cells running the longitudinal length of the monolith. The cross-sectional area of these through hole cells is extremely small, on the order of 10 microns. Wall flow monoliths are capable of trapping 99+ percent of the particulate emissions from a diesel engine. However, wall flow monoliths can become plugged very easily due to the very small openings of the through hole cells. As shown in FIG. 1, NO2 in the exhaust gas can be used to oxidize the carbon to form NO and CO, thus removing some of the particulate blocking the wall flow monolith. However, the amount of NO2 present in the exhaust gas from the diesel engine or generated in the flow-through monolith 22 may not be sufficient to completely oxidize the particulate blocking the wall flow monolith. Accordingly, the engine must be operated in order to generate substantial amounts of NO2 necessary to oxidize all the carbon and other particulate matter blocking the wall flow monolith. Otherwise, the wall flow monolith must be cleaned in another fashion.
Thus, it would be desirable to provide a filter system for a diesel engine which resulted in the wall flow monolith being plugged less often and providing an alternative means for regenerating the trap. The present invention overcomes deficiencies in the prior art and provides alternatives and advantages thereto.